Prior, when a solid substance is microencapsulated, the solid substance was dissolved with a solvent and then subjected to microencapsulation as a liquid core substance. However, the microencapsulation method has troublesome problems when the solid substance is insoluble or difficult to dissolve in available solvents. Namely, a specific solvent may be required or even if the microencapsulation can be successfully performed, a precipitation of the solid substance may cause to destroy the capsule walls.
On the other hand, as a microencapsulation method of biologically active solid substances, it is known that a pesticidal substance can be microencapsulated by the condensation-polymerization of methylolurea and/or methylolmelamine in the presence of both cationic urea resin and anionic surfactant (Japanese unexamined patent publications sho58-124705A and hei9-52805A). These methods comprise dispersing a core substance with an anionic surfactant or anionic dispersant and then forming resin wall at the surroundings of the core substance by the ionic binding force as melamine resin and urea resin have cation groups.
However these microencapsulation methods tend to cause an aggregation of core substance or microcapsules and it is difficult to obtain a uniform microencapsulated composition. And the microencapsulated compositions obtained by these methods also tend to aggregate by alterations in pH or in the presence of an ionic substance. Concerning pesticidal substances particularly, aggregating tendency depends on the hardness of the water utilized for diluting and there are problems of fluctuation of the effect of active ingredient and clogging at application.